title: Simultaneous multiple-excitation multiphoton microscopy yields increased imaging sensitivity and specificity.
abstract: BACKGROUND
  Multiphoton microscopy (MPM) offers many advantages over conventional wide-field and confocal laser scanning microscopy (CLSM) for imaging biological samples such as 3D resolution of excitation, reduced phototoxicity, and deeper tissue imaging. However, adapting MPM for critical multi-color measurements presents a challenge because of the largely overlapping two-photon absorption (TPA) peaks of common biological fluorophores. Currently, most multi-color MPM relies on the absorbance at one intermediate wavelength of multiple dyes, which introduces problems such as decreased and unequal excitation efficiency across the set of dyes.
  
  
  RESULTS
  Here we describe an MPM system incorporating two, independently controlled sources of two-photon excitation whose wavelengths are adjusted to maximally excite one dye while minimally exciting the other. We report increased signal-to-noise ratios and decreased false positive emission bleed-through using this novel multiple-excitation MPM (ME-MPM) compared to conventional single-excitation MPM (SE-MPM) in a variety of multi-color imaging applications.
  
  
  CONCLUSIONS
  Similar to the tremendous gain in popularity of CLSM after the introduction of multi-color imaging, we anticipate that the ME-MPM system will further increase the popularity of MPM. In addition, ME-MPM provides an excellent tool to more rapidly design and optimize pairs of fluorescence probes for multi-color two-photon imaging, such as CFP/YFP or GFP/DsRed for CLSM.
authors.affiliation: Department of Neuroscience and Biomedical Graduate Program, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA.
authors.forename: Margaret T
authors.initials: MT
authors.lastname: Butko
authors.forename: Mikhail
authors.initials: M
authors.lastname: Drobizhev
authors.forename: Nikolay S
authors.initials: NS
authors.lastname: Makarov
authors.forename: Aleksander
authors.initials: A
authors.lastname: Rebane
authors.forename: Brendan C
authors.initials: BC
authors.lastname: Brinkman
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Gleeson
mesh_terms: D000818:Animals; D002460:Cell Line; D002477:Cells / Q000378:metabolism; D006801:Humans; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D012680:Sensitivity and Specificity